A grain oriented electrical steel sheet is a material mainly utilized as an iron core of a transformer. A grain oriented electrical steel sheet is therefore required in terms of achieving high efficiency of a transformer and reducing noise thereof to have material properties including low iron loss properties and low magnetostrictive properties.
In this regard, it is important to highly accumulate secondary recrystallized grains of a steel sheet in (110)[001] orientation, i.e., what is called “Goss orientation.” However, too high a degree of accumulation of the secondary recrystallized grains in the Goss orientation is known to increase iron loss in a steel sheet. Therefore, there has been developed to solve this problem a technique of introducing strains and grooves into a surface of a steel sheet to subdivide the width of a magnetic domain to reduce iron loss, i.e., magnetic domain refinement technique.
For example, JP-B 57-002252 proposes a technique of irradiating a steel sheet as a finished product with a laser to introduce high-dislocation density regions into a surface layer of the steel sheet, thereby narrowing magnetic domain widths and reducing iron loss of the steel sheet. The magnetic domain refinement technique using laser irradiation was improved thereafter (see JP-A 2006-117964, JP-A 10-204533 and JP-A 11-279645 and the like), so that a grain oriented electrical steel sheet having good iron loss properties can be obtained.
There is a demand for further improvement of iron loss properties of a grain oriented electrical steel sheet due to increasing public awareness of energy-saving and environment protection in recent years. However, the grain oriented electrical steel sheets in JP '252, JP '964, JP '533 and JP '645 described above cannot necessarily possess satisfactory iron loss properties in this regard.
It could therefore be helpful to provide a grain oriented electrical steel sheet capable of causing an improved iron-loss reducing effect in reducing iron loss by controllably modifying magnetic domain structures through laser irradiation, as well as an advantageous method for manufacturing the grain oriented electrical steel sheet.